1. Field of the Invention
The invention relates to a method of roller spinning dynamically balanced cup-shaped metal stage blanks for subsequent use in spinning V-grooved pulleys by flow forming the blank metal in a series of continuous metal thinning operations with a plurality of improved rollers. The invention further relates to an improved roller construction for carrying out the steps of such a spinning method in which the roller is provided with a series of integrally joined metal deformation and expansion zones enabling large amounts of metal to be flow formed along a die form in a single roller pass.
2. Description of the Prior Art
Many procedures have been used and are known for the formation of cup-shaped metal blanks from flat sheet metal discs which blanks in turn are used in the manufacture of V-grooved pulleys, or similar articles. Many of these procedures involve stamping, drawing and slitting operations, examples of which are shown in U.S. Pat. Nos. 1,766,098, 2,330,228, 2,493,053 and 3,080,644. Cup-shaped stage blanks for V-grooved pulleys produced by such prior stamping and drawing methods are not balanced dynamically since the blanks are formed by a series of progressive die steps on a non-rotating blank.
Other procedures and apparatus have been known for directly spinning cup-shaped blanks and V-grooved pulleys from flat metal discs for producing dynamically balanced V-grooved pulleys, as shown in U.S. Pat. No. 1,728,002. The equipment and dies required, however, involves headstock dies with sliding and movable members which considerably increase the cost of pulley manufacture with such apparatus. Likewise, these dies require means on the machine for controlling movement of the die components which contribute to the increased costs and involve maintenance problems. Also, considerable tooling costs are involved to provide various dies from which to produce a variety of cup blanks, since a different die size and configuration is required for each type of cup blank produced.
Several other known procedures for spinning objects from flat sheet metal blanks are known, such as the procedure in U.S. Pat. No. 3,195,491 for spinning rounded bowl-like blanks from discs in producing tapered disc wheels. Conical-shaped metal objects are produced by roller spinning procedures in U.S. Pat. No. 3,104,640. The disc wheel or conical-shaped metal objects produced by such methods have tapered or curved side walls which are not suitable for V-grooved pulley manufacture. U.S. Pat. No. 3,282,078 uses tubular-shaped blanks instead of flat metal discs to spin grooved objects. This procedure flows the metal by thinning the sidewalls of the tubular blank to form an enlarged curved end groove.
Flow forming of metals has increased in importance in recent years in the production of many products formerly produced by stamping, extrusion drawing, etc. In the flow forming of metals, a relatively thick walled blank is placed on a rotating mandrel and is stretched and elongated to thin the metal by one or more rollers in one or more roller passes along the mandrel. The amount of metal reduction possible depends upon many factors such as the type of metal, power rating of the spinning machine, type and shape of the rollers, and number and speed of roller pases. The starting blanks may be drawn, pressed, forged and extruded, as well as open ended tubing. Preformed round sheet metal blanks also may be roller spun into a cup at the start of the roller passes and then flow formed in one and the same pass in forming the desired product.
Known roller constructions have various shapes and configurations depending upon the material to be flow formed, the degree of metal deformation and the type of blank (flat blank, pre-drawn blank, etc.) being worked. One of the common types of roller shapes has a front flow forming collar formed by a relatively long rearwardly outwardly tapered conical surface which terminates in a short rearwardly outwardly extending surface which in turn forms a single metal working corner with a rearwardly inwardly extending conical burnishing surface. Another type of roller which is used primarily for forming aluminum and other soft metals has a large radius configuration on the leading part of the roller for shaping a round blank into a cup followed by reduced diameter conical and cylindrical sections which are integrally joined with a trailing roller portion having the flow forming collar type configuration described above. Still another type of roller configuration, sometimes referred to as a conical roller, has a small rearwardly outwardly extending conical surface which forms a metal working corner with a following, rearwardly inwardly tapered conical surface.
All of these known roller constructions and methods for flow forming metal have and use only a single metal deformation or working surface. This requires multiple or slower roller passes along the rotating mandrel to achieve the desired amount of metal thinning, or requires more powerful and expensive spinning machines to achieve the desired thinning and elongation.
No known metal flow forming methods and improved roller construction for carrying out the steps of such a method to produce cup-shaped pulley blanks, of which I am aware, provides at least a pair of flow forming corners or surfaces separated by a metal relief zone on a single roller, whereby the metal is flow formed along a rotating mandrel by such a series of metal forming surfaces to provide greater movement of metal in a single pass than heretofore achieved.